Objectives are to evaluate the extent to which saturation of mast cell IgE binding sites occurs and the relevance of the phenomenon to human immediate hypersensitivity. Three related projects are proposed. (1) To compare the frequency and severity of immediate hypersensitivity reactions to common environmental antigens in populations otherwise similar, but differing greatly in the frequency of helminthiasis. (2) To examine changes in skin mast cell number and histamine content with age and to determine the topographical distribution of mast cells. (3) To compare the mast cell IgE binding capacity to the capacity of the mast cells to be sensitized for histamin release (in vitro) in skin excised from individuals with a wide range of IgE levels. Project (1) is a survey study of children of Mexican-American descent in Southern San Diego County compared with a similar group of Mexican children in nearby Tijuana. Helminthiasis will be determined by stool examination, IgE levels by a radioimmunosorbent-blocking assay and immediate hypersensitivity to common environmental antigens by skin tests. Project (2) will be done using histological techniques on skin samples derived coincident to surgery and from postmortem samples. Project (3) will be done on tissue samples derived coincident with surgical treatment and involves sensitization of skin slices with reaginic serum for antigen-induced histamine release, as well as microautoradiography using I125 IgE.